Solvent soluble aromatic polymides and production thereof

ABSTRACT

An aromatic tetracarboxylic acid which is representable by the general formula AND CONTAINS AT LEAST 30 MOL PERCENT OF AND A DIAMINE WHICH IS REPRESENTABLE BY THE GENERAL FORMULA H2NR&#39;&#39;-NH2 and contains at least 30 mol percent of diamines representable by any of   ARE HEATED AND CAUSED TO REACT IN SUBSTANTIALLY EQUAL MOL QUANTITIES IN A PHENOLIC SOLVENT OR IN AN APROTIC ORGANIC POLAR SOLVENT THEREBY TO PRODUCE A NEW LINEAR AROMATIC POLYIMIDE WHICH IS SOLUBLE IN ORGANIC SOLVENTS AND HAS HIGH STABILITY FOR PRESERVATION IN THE FORM OF SOLUTIONS SUCH AS VARNISHES. This method does not require a step of thoroughly dehydrating the aromatic tetracarbosylic acid component prior to the reaction.

United States Patent Suzuki et al.

[54] SOLVENT SOLUBLE AROMATIC POLYMIDES AND PRODUCTION THEREOF Shawa Densen Denran Kabushiki Kaisha a/k/a Showa Electric Wire & Cable Co., Ltd., Kanagawa-ken, Japan 22 Filed: Dec. 15,1969

211 Appl.No.: 885,140

[73] Assignees [30] Foreign Application Priority Data Dec. 14, 1968 Japan ..43/91760 [52] US. Cl ..260/33.4 P, 260/47 CZ, 260/78 TF [51] Int. Cl. ..C08g 20/00, C08g 5/44 [58] Field of Search ..260/78 TF, 47 CZ, 33.4 P

[56] References Cited UNITED STATES PATENTS 3,277,043 10/1966 Holub ..260/33.4 3,345,342 10/1967 Angelo ..260/78 3,493,540 2/1970 Muller ...260/47 3,501,443 3/1970 DiLeoneM ..260/78 3,505,168 4/1970 Dunphy 161/227 3,533,997 10/1970 Angelo ..260/47 Primary Examiner-Morris Liebman Assistant Examiner-Richard Zahlen Attorney-Holman & Stern May 30, 1972 [57] ABSTRACT An aromatic tetracarboxylic acid which is representable by the general formula HOOC HOOC

COOH

COOH

and contains at least 30 mol percent of H000 COOH and a diamine which is representable by the general formula H N-R'NH- and contains at least 30 mol percent of diamines representable by any of NH; Y

are heated and caused to react in substantially equal mol quantities in a phenolic solvent or in an aprotic organic polar solvent thereby to produce a new linear aromatic polyimide which is soluble in organic solvents and has high stability for preservation in the form of solutions such as varnishes. This method does not require a step ofthoroughly dehydrating the aromatic tetracarbosylic acid component prior to the reaction.

31 Claims, 9 Drawing Figures Patented May 30, 1972 3,666,709

3 Sheets-Sheet 1 FIG. I

mun mm 1500 won nun mo sou WAVE NUMBER mm") FIG. 2

4000 2mm mun nun man 1000 am 100 sun WAVE NUMBER mm") Y FIG. 3

4000 2000 1am) nuo man man sun mu suo WAVE NUMBER (cm' INVENTORJ 01. Suz UK" Er )94 BY MM M D 1 I '7 Adm,

Patented May 30, 1912 3,666,709

3 Sheets-Sheet 2 FIG. 4

PERCENTTHANSMlSSIQ! Q 2 f5 2 g 8 20011 1000 11011 1500 11100 01111 100 000 WAVE NUMBER (cm-'1 FIG. 5

51011 5300 I 2 011 g :40 Z 520 t 0 WAVE NUMBER (cm- 1 Fl G. 6

5100 00 2 200 E40 2320 a: a: 0

4000 2000 100111100 10011 WAVE NUMBER(Cm' INVENTORJ MJuzwn r/7z. naw; v W

Patented May 30, 1972 3,666,709

3 Sheets-Sheet 3 FIG. 7

PERCENTTRANSMISSIUN WAVE NUMBER (cm'H FIG. 8

200 1000 1700 1500 0,1000 000 100 000 WAVE NUMBER (Cm") FIG.9

1000 2000 1500 1000 000 WAVE NUMBER 1cm") INVENTORJ Mnfuzuki r 0L SOLVENT SOLUBLE AROMATIC POLYMIDES AND PRODUCTION THEREOF BACKGROUND OF THE INVENTION This invention relates generally to polyimides and more particularly to new linear aromatic polyimides which are soluble in organic solvents and, moreover have excellent stability when preserved as varnishes.

As synthetic resins capable of forming coating films having heat resistance, polyarnide acids prepared by causing an aromatic tetracarboxylic acid dianhydride and an aromatic diamine to undergo addition reaction in an aprotic organic polar solvent at a temperature below 50 C., preferably below 20 C. have been known.

By applying such a polyarnide acid in the form of a solution on an article such as an electrical conductor and heating the same, the solvent is evaporated off, and, at the same time, the solute is dehydrated and condensed to become a polyimide, whereby a coating film of excellent heat resistance is formed.

While polyarnide acids have such an advantage, they are extremely unstable and are gradually converted into insoluble polyimides even at room temperature, and a solution thereof thereby gels. For this reason, it is necessary to preserve these polyarnide acids by refrigeration and to use, as the reaction solvent, an expensive aprotic organic polar solvent. Consequently, varnishes prepared from these polyarnide acids become disadvantageously expensive.

By this reaction, furthermore, polymers of a high degree of polymerization can be obtained only in the case wherein the aromatic diamine is dissolved beforehand in the polar solvent, and the aromatic tetracarboxylic acid dianhydn'de is added gradually to this solution to cause reaction. When the addition sequence is reversed, or when the aromatic tetracarboxylic acid dianhydride is added as a solution, a polymer of a low degree of polymerization is formed, whereby the reaction operation becomes complicated. (References: 1. Polymer Sci., 1 (10) 3135-3150 (63), and 1. App. Polymer Sci., 11, 609-727 (67).)

By this known reaction method, moreover, when a tetracarboxylic acid is used in place of the tetracarboxylic acid dianhydride, the reaction does not progress. For this reason, it is necessary to heat and dry the tetracarboxylic acid dianhydride for a long time prior to the reaction, which procedure is 4 another difficulty accompanying this method.

In addition, US. Pat. Nos. 2,710,853, 2,731,447 and 2,900,369 disclose processes wherein an .aromatic tetracarboxylic acid and an aliphatic diamine are caused to undergo thermal reaction thereby to produce polyimides. These known aliphatic polyimides, however, are deficient in heat resistance and, moreover, have very low solubility in organic solvents, whereby it is not possible to use these polyimides as ingredients of varnishes.

A previous invention provides a process for producing curable liquid coating compositions in which carbonyl diphthalic acid anhydride and a diamine selected from the group consisting of diamines representable by the. general formula (wherein, R designates a divalent radical selected from the group consisting of C alkylene,

are heated in a phenolic solvent at a temperature below 160 C. (as disclosed in US. Pat. No. 3,277,043, granted Oct. 4, 1966 to Fred Holub).

The compositions obtained by this method, however, are polyarnide acids, and the polyimides obtained by dehydrating these polyarnide acids are insoluble. When carbonyl diphthalic acid is used as a starting material, the reaction proceeds with difficulty, whereby the necessity of a process step for fully dehydrating the carbonyl diphthalic acid anhydride prior to the reaction presents a problem.

In view of these various problems, we have carried out research thereon, whereupon we have made certain discoveries, as described hereinafter, which we have utilized in providing the polyimides and a method of producing the same according to the invention.

SUMMARY OF THE INVENTION It is an object of the present invention to utilize the findings we have made to provide'aromatic polyimides and a method of producing the same which are not accompanied by the above described difficulties.

More specifically, an object of he present invention is to provide linear aromatic polyimides which the soluble in organic solvents and, accordingly, have preservation stability when rendered into a solution.

Another object of the invention is to provide a method of producing linear aromatic polyimides which does not require a process step of thoroughly dehydrating the aromatic tetracarboxylic acid component used prior to the reaction for producing the polyimides.

As a result of our study, we have found that the above stated objects and other objects as will presently become apparent can be achieved by causing an aromatic tetracarboxylic acid which is representable by the general formula R HOOQ coon C 0 OH and contains at least 30 mol percent of nooc coon COOH to react in substantially equal mol quantities in a phenolic solvent-or in an aprotic organic polar solvent thereby to produce a linear aromatic polyimide of the above described desirable character.

The nature, details, and utility of the invention will be more clearly apparent from the following detailed description beginning with general considerations and concluding with specific example of practice constituting preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIGS. 1 through 9, inclusive, are infrared analysis charts of linear aromatic polyimides of the invention.

DETAILED DESCRIPTION A linear aromatic polyimide of the invention comprises one or more kinds of units representable by the general formula in at least 30 percent of which R is and, moreover, in at least 30 percent of which R' is one or more members selected from those representable by the general formulas Example of aprotic organic polar solvents suitable for use in the practice of the invention are N-methyl-Lpyrrolidone (NMP), N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMAc N,N-diethyl formamide (DEF), N- methyl formamide (NMF), dimethyl sulfoxide (DMSO), N,N- diethyl acetamide (DEAc), N,N-dimethyl methoxyacetamide (DMOA), hexamethyl phosphoramide HMPA), dimethyl sulfone (DMS), tetramethylene sulfone (TMS), and dimethyl tetramethylene sulfone (DMTMS in the case where a phenolic solvent is used, it is possible to use up to 20 to 30 percent of a non-solvent such as solvent naphtha, toluene, or xylene as a diluent after the process reaction.

A linear aromatic polyimide of the invention is produced as a clear solution, in general, by heating at a temperature of the order of from 100 to 240 C. one or more aromatic tetracarboxylic acids which are selected from tetracarboxylic acids representable by the general formula HO O C C O O H HO O C C O OH and in which the radicals R of at least 30 'percent of the tetracarboxylic acids are and one or more aromatic diamines which are selected from Examples of desirable forms of R other than those representable by the above set forth three general fonnulas are as follows.

aromatic diamines representable by the general formula H,N R' HN and in which the radicals R of at least 30 percent of the diamines are selected from among the fonns Examples of phenolic solvents suitable for use according to the invention are phenol, various cresols such as 0-, m-, and pcresol, various xylenols such as 2,3-xylenol, 2,4-xylenol, 2,5- xylenol, 2,6-xylen0l, 3,4-xylenol, and 3,5-xylenol, and halogenated derivatives thereof such as mono-, di-, tri-, tetra-, and penta-halophenols, mono-, di-, tri, and tetra-halocresols, mono-, di-, and tri-xylenol, examples of the halogens being Cl, Br, and l.

While, of the halogenated derivatives those which are in liquid state at room temperature are preferable, it is possible to use even those which are solids at room temperature by dissolving them in small quantities of aromatic hydrocarbons such as toluene and xylene and using the resulting solutions as solvents. However, since the reaction solvent, in general, is ultimately evaporated off, and halogenated phenol is ordinarily of higher price than non-halogenated phenol, it is preferable to use a non-halogenated phenol such as a phenol, cresol, or xylen ol.

matic diamines used as starting materials. We have found that, while the mixture mol ratio of the tetracarboxylic acid and the diamine or diamines is preferably one (unity), if it is within a range of from 0.9 to l. 1, an aromatic polyimide of sufficiently high molecular weight can be produced.

Furthermore, while the sequence in which the reactants are added is not subject to any restriction, the simultaneous use of a phenolic solvent and an aprotic organic polar solvent is not desirable.

The linear aromatic polimide solution obtained by this reaction may very somewhat in character depending on the kinds of solvent and starting materials used and the mixture proportions.

More specifically, when an organic polar solvent is used as the reaction solvent or one diamine or both diamines representable by from among the aforementioned three kinds of diamines is or are used, a clear polyimide solution is obtained in either case. However, in the case where a phenolic solvent is used as the reaction solvent, and only a diamine representable by from among the aforementioned three kinds of diamines is used, an opaque polyimide solution is obtained when the quantity of this diamine of from 30 to 60 mol percent with respect to the total quantity of aromatic diamines in the starting materials, and, at the same time, the quantity of the portion is of the order of from 30 to 55 mol percent of the total quantity of the aromatic tetracarboxylic acid.

However, this problem can be solved by increasing the proportion of the portion or by additionally using another diamine from among the above mentioned three aromatic diamines.

The reaction is carried out by two stages of dehydration and condensation as follows.

Since the product of the above indicated reaction is a polyi-' mide, this solution, differing from known products such as polyamide acids, is not accompanied by difficulties such as formation of water to produce foam or pinholes at the time of baking when used as a varnish.

We have found that when a small quantity of a catalyst such as a lower tetra-alkyl titanate, for example, tetrabutyl titanate or tetrapropyl titanate, is added to the solution during or after the reaction, the evaporation of the solvent at the time of baking of the varnish is promoted, and a baked coating film of exccllent surface state can be obtained.

Since, in accordance with the invention, the reaction is carried out at a high temperature, a tetracarboxylic acid, itself, can be used, and therefore there is no necessity whatsoever for a process step for drying the reactants prior to the reaction. However, this does not mean that a tetracarboxylic acid dianhydride cannot be used, it being possible, of course, to use dianhydrides of tetracarboxylic acids and lower alkylesters in a similar manner.

. ylether,

diaminobenzophenone,

Examples of compound components of aromatic tetracarboxylic acid suitable for use in the practice of the invention are 3,3,4,4'-benzophenonetetracarboxylic acid, pyromellitic acid, 3,3 ,4,4'-diphenyltetracarboxylic acid, 2,2',3,3'-diphenyltetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, bis (3,4-dicarboxyphenyl) ether, bis(3,4-dicarboxyphenyl) sulfide, bis(3,4-dicarboxyphenyl) sulfone, bis(3,4-dicarboxyphenyl) methane, bis(3,4-dicarboxyphenyl) propane, and anhydrides and lower alkylesters such as methyesters and ethylesters of these tetracarboxylic acids.

Examples of aromatic diamines representable by the three general formulas set forth hereinbefore are 3,3-dimethyl-4,4 '-diaminodiphenylmethane, 3,3'-diethyl-4,4'-diaminodiphenylmethane, 3 ,3 '-dimethoxy-4,4' -diaminodiphenylmethane 3,3'-diethoxy-4,4'-diamino diphenylmethane, 3,3-dichloro- 4,4'4,4-diaminodiphenylmethane, 3 ,3 '-dibromo-4 ,4 diaminodiphenylmethane, 3 ,3 '-dicarboxy-4,4'-diaminophenylmethane, 3,3 '-dihydroxy-4,4'-diaminophenylmethane, 3 ,3 disulpho-4,4'-diaminodiphenylmethane, 3 ,3 -dimethyl-4 ,4 diaminodiphenylether, 3,3-diethyl-4,4'-diaminodiphen- 3,3-dimethoxy-4,4-diaminodiphenylether, 3,3- diethoxy-4,4'-diaminodiphenylether, 3 ,3 '-dichloro-4,4- diaminodiphenylether, 3,3'-dibromo-4,4'-diamino diphenylether, 3,3'-dicarboxy4,4-diaminodiphenylether, dihydroxy-4,4-diaminodiphenylether, 3,3 -disulfo-4,4- diaminodiphenylether, 3 ,3 '-dimethyl-4,4-diaminodiphenylsulfide, 3 3 -diethyl-4,4 '-diaminodiphenylsulfide, 3 3 dimethoxy-4,4'-diamin0diphenylsulfide, 3,3 '-diethoxy-4,4 diaminodiphenylsulfide, 3 ,3 '-dichloro-4,4'-diaminodiphenylsulfide, 3,3-dibromo-4,4-diaminodiphenylsulfide, 3,3-dicarboxyl-4,4-diaminodiphenylsulfide 3 ,3 '-dihydroxy-4,4 diaminodiphenylsulfide, 3,3 '-disulfo-4,4-diaminodiphenylsulfide, 3,3'-dimethyl-4,4 '-diaminodiphenylsulfone, 3 ,3 diethoxy-4,4'-diaminodiphenylsulfone, 3,3'-dichloro-4,4- diaminodiphenylsulfone, 3 ,3 -dicarboxy-4 ,4 -diaminodiphenylsulfone, 3 ,3 '-dihydroxy-4,4'-diaminodiphenylsulfone, 3 ,3 disulfo-4,4'-diaminodiphenylsulfone, 3,3'-diethyl-4,4'- diaminodiphenylpropane, 3,3 -dimethoxy-4,4'- diaminodiphenylpropane, 3,3'-dibr0mO-4,4'-diaminodiphenylpropane, 3,3 -dichloro-4,4'-diaminodiphenylpropane, 3 ,3 dicarboxy-4,4-diaminodiphenylpropane, 3,3 -dihydroxy- 4,4'-diaminodiphenylpropane, 3 ,3 -disulfo-4 ,4- diaminodiphenylpropane, 3,3'-dimethyl-4,4- diaminobenzophenone, 3,3'-dimethoxy-4,4- diaminobenzophenone, 3,3'-dichloro-4,4- diaminobenzophenone, 3,3-dibromo-4,4- diarninobenzophenone, 3 ,3 -dicarboxy-4 ,4- 3,3'-dihydroxy-4,4-

diaminobenzophenone, 2,4-diaminotoluene, 2,6- diaminotoluene, l-isopropyl-2,4-phenylenediamine, 2,4- diarninoanisole, 2,4-diaminomonochlorobenzene, 2,4- diaminofluorobenzene, 2,4-diarninoben2oic acid, 2,4-

diaminophenol, and 2,4-diaminobenzenesulfonic acid.

I Examples of other aromatic diamines suitable for use in addition to the above set forth diamines are benzidine,3,3'- diaminodiphenyl, m-phenylenediamine, p-phenylenediamine, 4,4-diaminodiphenylmethane, 4,4'-diaminodiphenylether, 4,4'-diaminodiphenylsulfide, 4,4-diaminodiphenylsulfone, 4,4'-diaminodiphenylpropane, 3,3'-dimethylbenzidine, 3,3- dimethoxybenzidine. 3,3 -dichlorobenzidine, 3 ,3 dibromobenzidine, 3,3 -dicarboxybenzidine, 3 ,3 '-dihydroxybenzidine, and 3,3'--disulfobenzidine.

In the case where R consists of only and, moreover, R consists of only a member selected from the afore-mentioned three general formulas, the linear aromatic polyimide of the invention has the optimum solubility with respect to an organic solvent. As the other ingredients increase this solubility progressively decreases. On the other hand, when the proportion of the tetracarboxylic acid with R representable by increases, or when the proportion of those in which R is selected from the aforementioned three general formulas increases, the flexibility of the resulting resin ordinarily decreases.

Accordingly, to produce linear aromatic polyimides having both excellent solubility with respect to solvents and excellent flexibility, the respective proportions of the materials corresponding to R and R are suitably adjusted.

While the solubility of the polyimides of the present invention is higher in organic polar solvents of the aprotic class, in general, than in phenolic solvents, such organic polar solvents are considerably more expensive than phenolic solvents and, moreover, are toxic to humans.

We have found that in the case where is used for R, and a phenolic solvent is used as the reaction solvent, however, it is desirable that at least 55 percent of the radical R be representable by and at least 55 percent of the radical R be representable by In the case wherein these radicals are from 30 to 40 percent of R or R, linear aromatic polyimides of relatively low solubilities are obtained.

We have found further that, in order to obtain polyimides suitable for use in varnishes for production of so-called magnet wires, that is, linear aromatic polyimides having viscosities of from 40 to poises at room temperature in the form of solutions in a phenolic solvent of a resin content of 20 percent, it is desirable that at least 55 mol percent of the R in either of the above stated cases be Furthermore, when R is composed of from 55 to 65 percent and from 45 to 35 percent of caused to be and, at the same time, 50 percent or less of the remainder is selected from maximum solubility is obtained, and an inexpensive non-solvent such as toluene or xylene can be used as a diluent up to a maximum limit, that is, approximately 30 percent. Moreover, a very tough film can be formed from the resin thus produced. In all cases where R is HOOC COOH H the functional groups such as COOH or OH among the molecules can be connected by means of links such as diisocyanates to produce a cross-linked structure.

While the linear aromatic polyimide of the invention can be isolated by adding a large quantity of a non-solvent to the resin solution which is obtained as the reaction product, it is also possible when necessary to use the resin solution directly as a varnish by adding a modifier thereto.

In cases where the requirement for heat resistance is not very important, a portion of the aromatic diamine constituting a starting material can be substituted by an aliphatic diamine thereby to introduce an aliphatic radical into a portion of R. Introduction of an aliphatic radical, in general, increases the flexibility of the polyimide.

Examples of suitable modifiers are diisocyanates, stabilized isocyanates, and soluble polyester resins.

An isolated polyimide of the invention can be dissolved, if necessary, in a solvent and used thus as a varnish or it can also be used directly as a stabilizer for rubbers, synthetic resins, etc., as a filler in ceramics, and as a resin material for pressure molding.

The utility and advantageous features of the present invention as indicated above may be summarized as follows.

1. The linear aromatic polyimides of the invention are dissolved in the imide state in a solvent and, therefore, does not need to be refrigerated for preservation as a varnish. (In conmml. u sn cullctl polyimide varnish of known type is n solution of a polyumidc acid in a solvent and is gradually converted into an insoluble polyimide to precipitate unless it is preserved under refrigeration.)

2. A varnish in which a polyimide of the invention is used can be applied to fonn a clean coating film free of defects. (In contrast, when known polyimide varnishes are baked, foam or pinholes due to water from the polyamide acid tend to be formed in the resulting coating film.)

3. In accordance with the invention, it is not necessary to dehydrate thoroughly the tetracarboxylic acid dianhydride prior to the reaction as in known methods.

4. By the method of the invention, the reaction can be controlled in a relatively simple manner since a polymer of high degree of polymerization can be obtained irrespective of the order or method of addition of the starting materials.

5. By the practice of the invention polyimide varnishes of low price can be produced, and there is little risk of operators in the manufacture thereof being poisoned because almost all of the polyimides according to the invention are soluble in non-toxic and inexpensive phenolic solvents.

In order to indicate still more fully the nature and utility of the invention, the following examples of practice constituting preferred embodiments of the invention, the results thereof, and reference examples are set forth, it being understood that these examples are presented as illustrative only and that they are not intended to limit the scope of the invention.

EXAMPLE 1 A three-neck flask provided with a thermometer, an agitator, and a condenser was charged simultaneously with 32.2 grams (g.) (0.1 mol) of 3,3,4,4-benzophenonetetracarboxylic acid dianhydride, 22.8g. (0.1 mol) of 3,3-dimethyl-4,4- diaminodiphenylmethane, and 145 g. of m-cresol. The batch thus charged was heated, as it was agitated, from room temperature to 160 C., whereupon, water began to be produced gradually from within the reaction system, and the solution progressively became clear.

The heating and agitation process was continued for approximately one hour, and the reaction was stopped after the distillation of water stopped (distillate quantity 3.5 g.). To the resin solution thus obtained, acetone was gradually added to cause the resin content to precipitate. The precipitated resin was then washed and vacuum dried at room temperature, whereupon a polyimide resin of light yellow color was obtained in a quantity of 48.8 g. (95 percent yield).

This resin did not melt at 300 C., and the inherent viscosity thereof in m-cresol with a 0.5-percent concentration was 0.72. The infrared analysis chart of this resin is shown in FIG. 1, in which conspicuous absorptions are observable in the vicinity of 1,780, 1,730, and 730 cm, which are the characteristic absorption bands of imides.

The ultimate analysis (elementary analysis) of the resin as C H N (in percent) was, as theoretical values, 74.8 C, 4.2 H, and 5.4 N, and was, as measured, 73.6 C, 3.4 H, and 5.1 N.

Inherent viscosities as herein set forth were calculated from the following equation.

r solution viscosity wherein C is the polymer concentration expressed in number of grams per ml. of the solution, and the solution viscosity is the measured value of a 0.5-percent solution in m-cresol at 30 C.

The m-cresol used had the following composition.

% by weight p cresol 40.0 m cresol 53.7 0 cresol 2.5 phenol 3.8

The infrared analysis was carried out by the KBr wafer. The absorption indicated in the vicinity of 3,400 cm in the infrared chart of FIG. 1 is due to the moisture content of the KBr.

EXAMPLE 2 The procedure set forth in Example 1 was carried out with the same starting materials as specified therein and with DMAc as the reaction solvent, whereupon an aromatic polyimide in the form of a solution was produced and found to have characteristics similar to those of the product of Example 1.

EXAMPLE 3 A procedure similar to that of Example 1 was carried out with the following starting materials and solvent thereby to produce a linear aromatic polyimide.

The yield and characteristic of the linear aromatic polyimide thus produced were as follows.

Yield 95.5 Color light yellow Melting above 300C Infrared analysis (chart, FIG. 2

Solution clear Ultimate analysis as C H N O CI Theoretical (70): 65.4 C, 2.5 H, 5.0 N. Measured 64.6 C, 2.0 H, 4.8 N.

EXAMPLE 4 A procedure similar to that of Example 1 was carried with the following starting materials and solvent thereby to produce a linear aromatic polyimide.

3,3-4,4'-benzophenone 32.2 g.

tetracarboxylic acid (0.1 mol) dianhydride 3,3'-diaminodiphenylsulfone 24.8 g.

(0.1 mol) m-cresol g.

Reaction conditions C X 4 hours Quantity of water distilled 3.4 g.

The yield and characteristics of the linear aromatic polyimide thus produced were as follows.

gieild iii wire of a coating film thickness of 0.047 mm. was obtained.

O 01 lg t ye OW Melting point above 300C The characteristics of this magnet wire were as follows. Infrared analysis (chart, H6. 3) Solution clear 7 Ultimate analysis as C H O N S 5 P'F? f 0 Theoretical /2, 652C, 2.6H, 5.2 N. Flex'blmy (mmmuw Measured 64.8C, 2.2i-i, 5.2 N. wrap-around diameter) 1 x diam. good Abrasion, Repeating Scrape 700 g. load) 60 cycles EXAMPLES 5, 6, 7, 8, AND 9 C t-through temperature above (single-point crossing, Linear aromatic polyimides were produced respectively by H 700 2- procedures similar to that of Example 1 and with the starting eat Shock (300C x 1 t materials, solvents, and reaction conditions as set forth in 8 Table 1. The yields and characteristics of the resulting polyi- Breakdown voltage mide resins are also indicated in the same Table l. (Normal State 1&8

. TABLE 1 Example 6 6 7 8 11 Starting material (mol):

3,3,4,4"benzophen0ne tetracarboxylic acid 0. 1 0. 1 O. 1 O. 1 0. l 3,3-dimethoxy4,4-diaminodiphenylpropane ll. 1 8,3-dicarboxy-4,4-diaminodiphenylrnethane 0, l 3,3-dihydr0xy-4,4'-diaminodiphenylether 0. 1 3,3-diethoxy-4,4-diaminodipl1enylsulfide 0. 1 3,3-disulfo-4,4-diaminodiphenylmethane 0i 1 .Solvent (g.):

Xylenol for industrial use 160 150 160 N MP v 150 DMF 160 Reaction conditions:

Reaction temperature C) 160 150 170 170 160 Reaction time (hr. .t 3 3 l 2 3 Resin product characteristics:

Yield (percent) a 95 96 95 96 96 Melting point C.) 1 300 3100 1 300 300 1 300 Inherent viscosity 0 80 0.82 0. 75 1.10 0.91 Colour a, Infrared analysis chart a I Above. 2 Light yellow. 3 FIG. 4. Quantity oi water distilled: 6.9 g. Ultimate analysis as MHiBNgOQ. Theoretical (percent): 67.! C, 2.8K, 4.9 N. H Measured (percent): 66.7 C, 2,611, 4.5 N. Y 7

EXAMPLE l0 (After 24-hr. immersion i in water) [6.5 KV. A procedure similar to that specified in Example 1 was carg. ried out with the following starting materials and solvent 2 hrs') Freon 22 resistance 0d thereby to produce a linear aromatic polyimide solution.

V EXAMPLES ll, l2, l3, l4,AND l5 3,3,4,4' benzophenone 322 g.

tetracarboxylic acid 1 mol) By a procedure similar to that of Example 1 and with the use dianhydfide of the starting materials set forth in Table 2, polyimide soluy ,f 137 8- tions were respectively produced. The polyirnides were iso- 4 g; figg ggl mg mm) lated from a portion of these solutions and subjected to in- (Q4 frared analysis, whereupon conspicuous absorptions were ob Xylem! for industrial use ,1 2' served in all cases in the vicinity of 1,780, 1,730, and 730 Reaction conditions 170C X 2 hrs.

cm", which are the characteristic absorption bands of imides.

TABLE 2 Example 11 12 13 14 15 Starting material (moi):

3,3,4,4-benzophenoi1etetracarboxylic acid dianhydride 1 1 1 1 1 3,3-diethyl-4,4-diziminodiphenylsulfone 7 3,3-dimethoxy-4,4 -dia.minodiphonyletlier 3,3'-dicarboxyl,4-diaminodi phonylsulfide. 3,3'-dihydroxy-4,4-diaminodiph en ylpropane. 3,3-diaminodiphenylpropanc 3,3-diaminodiphenylmethane" 4,4-diamin0diphenylmethania 4,4-diaminodiphenylethcr. Benzldine These solutions were than adjusted to a resin content of 20 percent and were respectively applied directly as coating on annealed copper wire of 1.0 mm. diameter and baked similarly as in Example 10, whereupon magnet wires of a coating film thickness of 0.047 mm. were obtained. The characteristics of the magnet wires thus produced are set forth in Table 3.

TABLE 3 Example 11 12 13 14 15 Test:

Pinholes (number/ in.) 0 0 0 0 Flexibility (wrap around own diameter) (good, poor) Good Good Good Good Good Abrasion, repeated scrape (700 g. load) (cycles) 144 156 160 168 Cut-through temperature (single-point crossing,, 700 g. load) 0.). 300 500 300 300 300 Heat shock (300 C.X2 hrs.) Breakdown voltage (KY):

Normal state 16. 7 16.5 16. 9 16. 7 16. 4 After 24-hr. immersion in water 16. 2 After heating, 200 C.X2 hrs 16. 3 Freon 22 resistance G d IX diameter, good.

EXAMPLE 16, 17,18 19, 20, AND 21 The procedure of Example 1 was carried out with the use of the starting materials set forth in Table 4 to produce respective polyimide solutions. After adjustment to a resin content of percent, these solutions were applied directly as coating an annealed copper wire of 1.0 mm. diameter and baked similarly as in Example 10, whereupon magnet wires of coating film thickness of from 0.047 to 0.048 mm. were obtained. The characteristics of these magnet wires are indicated in Table 5.

TABLE 4 The yield and characteristics of the linear aromatic polyimide thus produced were as follows.

Yield 94.7 Solution light yellow, clear Infrared chart (FIG 6) To this resin upon completion of the reaction, 2 g. of tetrabutyl titanate was added at room temperature, and the Example Starting material (mol):

3,3,4,4"benzophenone tetracarboxylic acid dianhydride Pyromellitie acid dianhydride 3,3,4,-1-diphenyltetracarboxylicaeid;i1:II::::::::::::::::::::. ,3,6,7-naphthalene tetracarboxylic acid dianhydride TABLE 5 Example 16 17 18 19 20 21 Test:

Pinholes (number/5 m.) 0 0 0 0 0 0 Flexibility (wrap around mm diameter) (good, poor) Good Good Good Good Good Good Abrasion, repeated scrape (700 g. load) (cycles) 82 90 87 80 102 112 Cut-through temperature (single-point crossing, 700 g. load) 300 300 300 300 300 300 Heat shock, (300 C.X2 hrs.) Breakdown voltage, (KY):

Normal state 16.5 16. 4 16.7 16.5 16. 3 16. 8 After 24-hr. immersion in water 16.1 16. 2 16. 4 16. 4 16. 0 16. 6 Alter heating, 200 C.X2 hrs... 16.0 16.0 16. 5 16.1 16.0 16. 5 Freon 22 resistance Good Good Good Good Good Good Infrared analysis chart 1 lxdiameter, good. 1 FIG. 5.

The polyimides were isolated from portions taken from the polyimide solutions obtained in the above described manner, and the characteristics of these isolated polyirnides were measured. All of these resins had a light yellow color and melting points above 300 C. Furthermore, the infrared analysis chart of each polyimide exhibited conspicuous absorptions in the vicinity of 1,780, 1,730 and 730 cm, which are the characterisu'c absorption bands of irnides. The inherent viscosities of these resins were as indicated in Table 4.

resulting mixture was agitated. The resulting varnish was applied as a coating directly on an annealed copper wire of 1.0

this magnet wire were as follows.

Pinholes (number/5m.) none) Flexibility (minimum wraparound diameter) 1 X diam. EXAMPLE 22 Abrasion. Repealed Scrape (700-g. load) (cycles) 120 The procedure of Example 1 was followed with the use of fut-tlhrough temperatu7r30 I ad) 300%:

sing e-point crosmg, g. 0 over the following starting materials and solvent, whereupon a Heat shock (300C X 2 his) I X diam" good linear aromatic polyirmde was obtained. Breakdown vohage (normal state) 16.5 KV 3,3',4,4'-benzophenone tetra 322 g. (after 24-hr. immersion in water) 16.0 KV

carboxylic acid dianhydride (1 mol) (after heating, 200C X 2 hlS.) 16.4 KV 3,3'-diaminodiphenylsulfone 124 g. Freon 22 resistance good (0.5 mol) 4,4'diaminodrp henyl th e (Q5 E EXAMPLES 2s, 24, 25,26, 27, AND 28. my I 1,500 is conditions C X l g The procedure of Example 1 was carned out with the start- Quantity of water distilled 3.3 g. 75 ing materials and solvents indicated in Table 6 thereby to produce linear aromatic polyimides, the characteristics of Abrasion, Repeating Scrape cycles (700 i loud) 7 which are shown in the same Table 64 Cut-through temperature 74 TABLE 0 Example 23 .24 25 27 28 Starting material (moi):

3,3,4t,4-henz0phenone tetracarboxylic acid .i (l. 07 0. 02 0.08 (l. 09 0. 0S 0. 07 Iyromellitic acid 3 3,3,4,4'-diphenyl tetracarboxylic acid. 0.01 0. ()3 2,3,6,7-naphthalene tetracarboxylic acid. 2,2-bis(3,4-dicarboxyphenyl) propane. r 3,3-diaminodiphenylsulfone 3,3-diaminodiphenylmothanc; o t 3,3-diaininodipheylsulfide 4 2,4-diamil1otoluene r 4,4-diaminodiphenylinotllone Benzidinc 1,5-diaminonaphthaleno. 3,3'-dimethyl-4,4-diamin v Xylenol for industrial use (g.) I50 150 lfil Reaction catalyst and quantity added (percent of resin iontont) r. r. r r r. r Reaction conditions (tempxtime) i 190 1S0 1S0 Yleld, (percent) EH. -l 03. Q 94. O Inherent logarithmic viscosity 0.70 0. 710 0. '70 Infrared analysis chart r a r Quantity of water distilled (g.) or

I Lead naphthanate. 2 'y-picoline. 3 C.X2 hrs. 4 (LXI hr. a FIG. 7. r

(single-point crossing. 700g. load) 300C 300C EXAMPLE 29 Heat shock (300%: x 2 hrs) l X diam- 1 X diam- With the use of the following starting materials and solvent, good th d re f E am le 1 was carried out to reduce a Breakdown vonage (Kv) I e Proce u o X p (Normal state) linear aromatic polyimide, to which a small quantity of Aft 24m i r i petroleum naphtha was then added to prepare an enamel 30 ft water) 12-: 12-:

' (A er eating, varnish of 20 percent resin content 200C X 2 hrs Aging test 1 X diam. 3 X diamv 3,3',4,4'-bcnzophenone tetracarboxylic (250C X 6 hrs. heating good good acid dianhydride 0.55 me! then wrapping) Pyromellitic acid dianhydride 0.45 moi Overload test (time for 3,3'-diaminodiphenylsulphone 0.40 mol ZO- A l ka e current to flow 4,4'-diaminodiphenylether 0.60 mol wh n 40-A current is passed through Xylenol for industrial use 1,500 g. twist pair sample) 30-5 10-15 Tetrabutyl titanate 0.44 g. min. min.

(0.1% of resin content) Reaction conditions 170C x 1 hr. 40 In the above mentioned comperison example, a polyimide ouam'ly was produced in the same manner as in Example 29 with equal mol quantities of 3,3',4,4'-benzophenone tetracarboxylic acid The enamel vamlsh thus Prepares wflspphed as a coawlg dianhydride and 3,3'-diaminodiphenylsulfone and applied as on an annealed copper wire of l.O mm. diameter and baked in coating and baked on an electrical conductor under the me same manner described ExamPle 10 PX to conditionsas in Example 29 to produce amagnet wire. The in Produce a magnet havmg the following Fhzfractensucsi herent viscosity of the polyimide of this Example 29 was 0.78 the results of a comparison example being also indicated. and the infrared analysis Chan is shown in RC 8 EXAMPLES 30, 3 l 32, AND 33 Example Comparison L I 29 Example Linear aromatic polyimides were obtained similarly as described in Example 1 through the use of the starting materials and solvents indicated in Table 7. The yields and inherent Pinholes (number/5 m,) 0 0 fth h b d a] f M Flexibilit (minimum viscosities o e p0 yiml es us 0 tame are so set 0 in wrap-around diameter) l X diam. l X diam. Table 74 TABLE 7 Example 30 31 32 33 Starting material (moi):

3,3,4,4benzophenone totracarboxylic acid dlanhydridc. 0. 0,30

3,3,4,4'-benzophenone totracurhoxylic acid methylester A Bis (3,4-dicarboxydiphon l) sulfone Bis (3,4-dicarboxyphenyl other 3.3-diamlnodiphenylpropaua. 3,3dlamlnodiplienylsuHone. 2,6-diamlnotoluene, 2,4-diamlnotol one, 20/ 4,4-diaminodiphenylpropane 4,4-diaminodiphenylmethanm 4,4-dizirnlnodlphenyletller 4,4'-diarninodiphenylsulione rn-Pheriylenediamlne 0. 25 Xylenol [or industrial use (g.) 1,600 1,500 1,500 1, 500 Reaction catalyst and quantity added (percent of resin content) 1 (L 0 l 0.1 Reaction conditions (temlxtime). 3 1 170 3 170 Yield, (percent) r o 95. 0 95. 5 96.0 Inherent viscosity 0.81 0. 79 0. 91 1.02

l Lead naphtllanate.

2 C. X 2 rs.

3 C. X 1 hr.

Nora-The 3,3,4,4'-benzophenone tetracarboxyllc acld methylester is 0! an acid value oi 231.4 (corresponding to dimethylestcr'). I p

17 l8 EXAMPLES 34. 35, 36, AND 37 EXAMPLE 44 With the use of the starting materials set forth in Table 8, A linear aromatic polyimide was produced with the followpolyimide solutions were obtain by a procedure similar to that ing starting materials and solvent by a procedure similar to of Example 1, and with these polyirnide solutions, enamel 5 hat fEXampl lvarnishes of ZO-percent resin content were prepared similarly as in Example 10.

TABLE 8 Example 34 36 36 37 Starting material (moi):

' 3.4,4-l)cuz0phcn0nc tctracarboxylic acid dlanliydride 1 .4

The enamel varnishes thus prepared were applied as coating 3 3 4 4 tr 32.2 g.

and baked on soft copper wires of LO-mm. diameter. The carboxylic acid dianhydride (0.l mol) magnet wires thus obtained had coating film thicknesses of 'dam'mbenmphemne 3' from 0.047 to 0.048 mm. and characteristics as indicated in xylene] for industrial use |5O Tab e 9 Reaction conditions 170C X 1 hr.

All polyimides of these examples had melting points above 300 C., and the inherent viscosities thereof were from 0.81 to The yield and characteristics of the linear aromatic polyil.20 (OS-percent concentration in DMAc, C. 30 mide thus produced were as follows.

TABLE 9 Example a3 an 37 Test:

Pinholcs (number/5 m.) i. 0 0

Wrap around own tlianicter (good/poor) Abrasion repeating scrnpo 700 load (uy v 0) 84 Cut through tonipia'aturn (single-point closslng, 700 g. load) C.) s, 300 300 300 300. limit chock, 300 (l.X2l1|S .7 c lircakdown voltagn, (KV):

Normal st tc AltcrtlHu's. imnmrsion in watm;

Altar heating 200 (1.)(2 hrs. Freon 22 resistant-u." c t s u lnfrarcd analysis chart V s V V i i t 1 1X diameter, good. 2 FIG. J.

4 4 Yield EXAMPLES AND 3 Quantity of water distilled I 35 3. d e Solution A light yellow. clear Lin ear aromatic polyimides were pro uced M h th start ng 50 Making point above 300C materials and solvents shown in Table 10 in a manner similar. lnhemnl viscosity Q86 to that of Exam le I. The results shown in the same Table 10. Examples 5, 4 7, 4g, 49, so, and 5 I.

TABLE 10 Example a; 3s 3'. 40 41 42 43 Starting material:

3,3,4,4-benzophenonc tetracarboxylic acid 0. 07 3,3 ,4,4'-benzophcnono tetracurboxylic acid 0.-1

Pyroinellitic acid 3,3,4,4-diphenyl tetracarboxylic acid 2,3,6,7-nephtha.lene tetracarboxylic acid, 2,2-bis (3,4-dicarboxypheny1) propane" 2,4-diaminoaniso1e s. 2,4-diaminomonochlorobenzene 2,4-diarninobenzoic acid 2,4-diarninophenol 2,4-diaminobenzenesulfonic ac 4,4-diaminodiphenylothcr 4.4-diaminodiphenylmcthano. Benzidine 4,4-diamino phenylpropane 1,5-diaminonaphthaleue Xylonol for industrial use (g.)

15 150 ni-Cresol (g.) 150 Reaction catalyst and quantity added (percent of resin content) 1 0. Reaction conditions ttcmnxtimc) Yicltl, tpcrccnt) lnhcrnnt viscosity s s A 19 20 With the starting materials and solvents indicated in Table l 1, linear aromatic polyimides were produced by a procedure and similar to that of Example I. The yields and characteristics of the resulting polyimides are also set forth in Table l 1.

TABLE 11 Example 45 46 47 48 4!) 50 5].

Starting material (moi):

3,3,4,4'-benzophenone tctracarboxyiic acid dianhydrido 0. 1 0.1 0.07 0.08 0.06 3.3,4.-t-benzophenone tetracm'boxylic acid dimethylostu 0.02 V 7 0,08 0. 07 Pyi'omcliitic acid diahydridv... 0.03 0.02 Bis(3.4-dicarbxyphenyl)etliul; A 3,3dimethyl-i,-i-diaminobcnzophenoue 0.015 3,3-dibromo-1,4'-di:1niinobonzophenoi1e. i. V 3,3"diox vL,-1-dimninobcnzoplwnoim. 3,3-dimetboxy- 1,4-dianiinobcnzophei1on0. 3,3-diaminobenzophenone A 4,-1-dian1in0diphenylmethone. 4,-diaminodiphenylether 0.04 4,*l-diaminodiphenylpropane 4,tf-diaminodiphenylsulione p-Phenylenediamine Benzidine 4 Xylenol for industrial use (g.) r.

DMAc (g.) i 4 i NMP (gm) 4 i A A Reaction conditions (temp.Xtime) 1 160 1 160 2 170 2 1 Yield (percent) 91.5 95.0 216.0 J4. 8 93.2 95.3 "4.

Inherent viscosity (L 78 0. 86 0. 75 0. ill 0. 71 0. 70 0. 89

REFERENCE EXAMPLE and R is selected from the group consisting of:

The following starting materials and solvent were caused to Y Y react at 125 C. for 3 hours to obtain a clear varnish, which was applied and baked on a copper plate. The resulting coat- X,

ing film of ZO-micron thickness was bent through i80 of angle, whereupon cracks were formed therein. Furthermore, when this varnish was caused to react at 170 C. for 3 hours, and the resin content thereof precipitated out. R

3,3',4,4'-benzophenone tetral6.l g.

carboxylic acid dianhydride (0.05 mol) at least 30 percent of the radicals R being representable by 4,4'-diaminodiphenylether g.

(0.05 mol) m-cresol 180 g. E

What we claim is: l. A linear aromatic polyimide consisting of units of at least one kind representable by the general formula at least 30 percent of the radicals Rbeing of at least one kind selected from the group consisting of radicals representable by selected from the group consisting of: 7 x i V,

"-v 4 V .V...... v t l where X is a member selectedfrom the group consisting of V i (2H3 CH -o-, s -s 02-, -c-', and -C,

- l l V 3H y 7 m I and Y is a member selected from the group consisting of lower aikyls, lower alkoxyis, halogens, COOH, OH and 80 K, said 55 poiyimide being in the form of a clear solution of a concentration'of more than l0 percent by weight thereof in a phenolic solvent and having an inherent viscosity of 30 degrees C, 0.5 g./ l 00 ml. in m-cresol greater than 0.05.

2. A linear aromatic polyimide as claimed in claim I in a which at least 30 percent of the radicals R is selected from s A is i 3 Cu 3,666,709 21 22 and said solvent is a phenolic solvent, in which the polyimide and from 45 to 35 percent of the radicals R is is dissolved to form a clear solution.

3. A linear aromatic polyimide as claimed in claim 1 in which at least 55 percent of the radicals R is o 7. A linear aromatic polyimide as claimed in claim I in which the radicals R are selected from those representable by HOOC COOII at least 55 percent ofthe radicals R is X i and said solvent is a phenolic solvent, in which the polyimide is dissolved to form a clear solution.

4 A linear aromatic polyimide as claimed in claim 2 in A linear aromatic polyimide as claimed in Claim 5 in which at least 55 percent of the radicals R is which from 5 5 to 65 Percent Oflhe radicals R is v A C 5. A linear aromatic polyimide as claimed in claim 2 in f t 35 e ce t of the radical is which from 55 to 65 percent of the radicals R is 35 at least percent of the radicals R is and from 45 to 35 percent of the radicals R is G G representable by i and the remainder of the radicals R is selected from radicals 6. A linear aromatic polyimide as claimed in claim 3 in 45 and 9. A linear aromaticpolyimide as claimed in claim 1 which which from to percent of the radicals R is t 7 W consists of recurring units each representable by Wm E E CH3 consists of recurring units each representable by 11. A linear aromatic polyimide as claimed in claim 1 which consists of recurring units each representable by ff nooo cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent byweight.

COOll 13. A linear aromatic polyimide as claimed in claim 2 in which the radicals R consists of radicals and the radicals R consists of 50 percent of radicals and 50 percent of radicals nooc coon and at least one diamine selected from the group consisting of aromatic diamines each representable by the general formula [H N R NH ]H N R Ni-L at least 30 percent of at least 30 percent of tE radicals R being representable by the radicals R being selected from the group consisting of radicals representable by in a phenolic solvent and heating the resulting solution at a temperature above the boiling point of water for a time period sufficient for occurrence of imide ring closure reaction.

15. A method of producing a linear aromatic polyimide as claimed in claim 14 in which said at least one selected aro- 19. A composition comprising a solution of an aromatic polyimide as claimed in claim 2 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.

20. A composition comprising a solution of an aromatic polyimide as claimed in claim 3 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.

21. A composition comprising a solution of an aromatic polyimide as claimed in claim 4 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.

22. A composition comprising a solution of an aromatic polyimide as claimed in claim 5 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.

23. A composition comprising a solution of an aromatic polyimide as claimed in claim 6 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.

24. A composition comprising a solution of an aromatic polyimide as claimed in claim 7 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight. I

25. A composition comprising a solution of an aromatic polyimide as claimed in claim 8 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.

26. A composition comprising a solution of an aromatic polyimide as claimed in claim 9 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.

27. A composition comprising a solution of an aromatic polyimide as claimed in claim 10 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at

a concentration of at least 10 percent by weight.

28. A composition comprising a solution of an aromatic polyimide as claimed in claim 11 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.

29. A composition comprising a solution of an aromatic polyimide as claimed in claim 12 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight. 30. A composition comprising a solution of an aromatic polyimide as claimed in claim 13 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.

31. A composition comprising a solution of an aromatic polyimide as claimed in claim 17 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight. 

2. A linear aromatic polyimide as claimed in claim 1 in which at least 30 percent of the radicals R'' is selected from and said solvent is a phenolic solvent, in which the polyimide is dissolved to form a clear solution.
 3. A linear aromatic polyimide as claimed in claim 1 in which at least 55 percent of the radicals R is at least 55 percent of the radicals R'' is and said solvent is a phenolic solvent, in which the polyimide is dissolved to form a clear solution.
 4. A linear aromatic polyimide as claimed in claim 2 in which at least 55 percent of the radicals R is
 5. A linear aromatic polyimide as claimed in claim 2 in which from 55 to 65 percent of the radicals R is and from 45 to 35 percent of the radicals R is
 6. A linear aromatic polyimide as claimed in claim 3 in which from 55 to 65 percent of the radicals R is and from 45 to 35 percent of the radicals R is
 7. A linear aromatic polyimide as claimed in claim 1 in which the radicals R'' are selected from those representable by
 8. A linear aromatic polyimide as claimed in claim 5 in which from 55 to 65 percent of the radicals R is from 45 to 35 percent of the radicals is at least 50 percent of the radicals R'' is and the remainder of the radicals R'' is selected from radicals representable by
 9. A linear aromatic polyimide as claimed in claim 1 which consists of recurring units each representable by
 10. A linear aromatic polyimide as claimed in claim 1 which consists of recurring units each representable by
 11. A linear aromatic polyimide as claimed in claim 1 which consists of recurring units each representable by
 12. A linear aromatic polyimide as claimed in claim 1 which consists of recurring units each representable by
 13. A linear aromatic polyimide as claimed in claim 2 in which the radicals R consists of radicals and the radicals R'' consists of 50 percent of radicals and 50 percent of radicals
 14. A method of producing a solution of a linear aromatic polyimide as defined in claim 1 which comprises the steps of dissolving substantially equal mol quantities of at least one compound selected from the group consisting of aromatic tetracarboxylic acid compound each representable by the general formula at least 30 percent of the radicals R being representable by and at least one diamine selected from the group consisting of aromatic diamines each representable by the general formula (H2N - R - NH2)H2N - R'' - NH2, at least 30 percent of the radicals R'' being selected from the group consisting of radicals representable by in a phenolic solvent and heating the resulting solution at a temperature above the boiling point of water for a time period sufficient for occurrence of imide ring closure reaction.
 15. A method of producing a linear aromatic polyimide as claimed in claim 14 in which said at least one selected aromatic tetracarboxylic said compound is a dianhydride.
 16. A method of producing a linear aromatic polyimide as claimed in claim 14 in which the aromatic diamine used does not contain any of OH, COOH, and SO3H as a substituent.
 17. A linear aromatic polymide as claimed in claim 1 wherein Y is selected from the group consisting of lower alkyls, lower alkoxyls, halogens, and -SO3H.
 18. A composition comprising a solution of an aromatic polyimide as claimed in claim 1 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 19. A composition comprising a solution of an aromatic polyimide as claimed in claim 2 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 20. A composition comprising a solution of an aromatic polyimide as claimed in claim 3 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 21. A composition comprising a solution of an aromatic polyimide as claimed in claim 4 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 22. A composition comprising a solution of an aromatic polyimide as claimed in claim 5 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 23. A composition comprising a solution of an aromatic polyimide as claimed in claim 6 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 24. A composition comprising a solution of an aromatic polyimide as claimed in claim 7 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 25. A composition comprising a solution of an aromatic polyimide as claimed in claim 8 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 26. A composition comprising a solution of an aromatic polyimide as claimed in claim 9 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 27. A composition comprising a solution of an aromatic polyimide as claimed in claim 10 homogeneouSly dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 28. A composition comprising a solution of an aromatic polyimide as claimed in claim 11 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 29. A composition comprising a solution of an aromatic polyimide as claimed in claim 12 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 30. A composition comprising a solution of an aromatic polyimide as claimed in claim 13 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight.
 31. A composition comprising a solution of an aromatic polyimide as claimed in claim 17 homogeneously dissolved in a phenolic solvent selected from the group consisting of phenol, cresol, xylenol and halogenated derivatives thereof, at a concentration of at least 10 percent by weight. 